Factors Affecting Bromus Tectorum Seed Bank Carryover in Western Utah

Cheatgrass (Bromus tectorum L.) is a winter annual weed that presents a serious obstacle to rangeland restoration in the Intermountain West. The objective of this study was to evaluate factors regulating the size and persistence of cheatgrass carryover seed banks on semiarid sites in western Utah. We prevented current-year seed production in each of four habitats, then tallied emerging seedlings over the next 44 yr. Twoyr. Two iterations of the study were conducted during consecutive years. One year before initiation of each iteration, we estimated seed rain at each site. Above-average precipitation in 1998–1999 resulted in relatively high seed rain (13942 seeds·m⁻²) for the first iteration, whereas seed rain for the second iteration averaged only 3567·m⁻² because of drought conditions in 1999–2000. Mean total number of seedlings emerging from carryover seeds for the first and second iterations were 1304 and 270 seedlings·m⁻². Seedling emergence from carryover seed was positively correlated with production-year seed rain (R² = 0.69). The fraction of seed rain that carried over tended to be lower when precipitation the year following production favored fall emergence of the transient seed bank. First-year emergence of carryover seeds averaged 96% of total emergence, whereas third-year emergence averaged < 1% and was zero for six of eight cases. Carryover seeds persisted somewhat longer at the xeric black greasewood site than at more upland sites. Our study shows that cheatgrass seeds rarely persist beyond the second carryover year even on semiarid sites. Emergence from the carryover seed bank can be predicted from site attributes and precipitation patterns in previous years.     

Intermountain Presettlement Juniper: Distribution,Abundance, and Influence on Postsettlement Expansion

Successful implementation of watershed restoration projects involving control of piñon and juniper requires understanding the spatial extent and role presettlement trees (> 140 yr) play in the ecology of Intermountain West landscapes. This study evaluated the extent, abundance, and spatial pattern of presettlement western juniper (Juniperus occidentalis Hook.) in four woodlands located in southeast Oregon and southwest Idaho. The potential for modeling presence/absence of presettlement juniper using site characteristics was tested with logistic regression and the influence presettlement trees had on postsettlement woodland (trees < 140 yr) expansion was evaluated with a Welch’s t-test. Pre- and postsettlement tree densities, tree ages, site characteristics, and understory vegetation were measured along four 14–27 km transects. Presettlement juniper occurred in 16%–67% of stands in the four woodlands and accounted for 1%–10% of the population of trees > 1 m tall. Presettlement trees were generally widely scattered and more common in lower elevation stands with greater surface rock cover and higher insolate exposure. Presettlement trees sparsely occupied productive sites on deeper soils in southwest Idaho, suggesting the area had sustained a different disturbance regime than southeast Oregon. Southwest Idaho might have experienced a high frequency of lower severity fire that afforded survival to widely distributed legacy trees. This supposition is in contrast to most reports of a disturbance regime including either stand replacement or frequent fire of sufficient intensity to preclude survival of trees to maturity. Stands sustaining presettlement trees initiated woodland expansion 24 yr earlier than stands lacking presettlement trees. Presettlement trees may serve as a seed source potentially reducing the longevity of juniper control treatments. For areas with greater abundances and spatial distribution of presettlement trees such as southwest Idaho, management maintaining low intensity fire or cutting treatments at frequencies of less than 50 yr should sustain relatively open stands.     

Medusahead Dispersal and Establishment in Sagebrush Steppe Plant Communities

Medusahead (Taeniatherum caput-medusae [L.] Nevski) is an invasive annual grass that reduces biodiversity and production of rangelands. To prevent medusahead invasion land managers need to know more about its invasion process. Specifically, they must know about 1) the timing and spatial extent of medusahead seed dispersal and 2) the establishment rates and interactions with plant communities being invaded. The timing and distance medusahead seeds dispersed from invasion fronts were measured using seed traps along 23 35-m transects. Medusahead establishment was evaluated by introducing medusahead at 1, 10, 100, 1 000, and 10 000 seeds · m⁻² at 12 sites. Most medusahead seeds dispersed less than 0.5 m from the invasion front (P < 0.01) and none were captured beyond 2 m. Medusahead seeds dispersed from the parent plants from early July to the end of October. More seeds were trapped in August than in the other months (P < 0.01). Medusahead establishment increased with higher seed introduction rates (P < 0.01). Medusahead density was negatively correlated to tall tussock perennial grass density and positively correlated to annual grass density of the preexisting plant communities (P = 0.02). Medusahead cover was also negatively correlated with tall tussock perennial grass density (P = 0.03). The results suggest that containment barriers around medusahead infestations would only have to be a few meters wide to be effective. This study also suggests that promoting or maintaining tall tussock perennial grass in areas at risk of invasion can reduce the establishment success of medusahead. Tall tussock perennial grass and annual grass density, in combination with soil data, may be useful in predicting susceptibility to medusahead invasion.     

Comparison of Medusahead-Invaded and Noninvaded Wyoming Big Sagebrush Steppe in Southeastern Oregon

Medusahead (Taeniatherum caput-medusae [L.] Nevski) is an exotic, annual grass invading sagebrush steppe rangelands in the western United States. Medusahead invasion has been demonstrated to reduce livestock forage, but otherwise information comparing vegetation characteristics of medusahead-invaded to noninvaded sagebrush steppe communities is limited. This lack of knowledge makes it difficult to determine the cost–benefit ratio of controlling and preventing medusahead invasion. To estimate the impact of medusahead invasion, vegetation characteristics were compared between invaded and noninvaded Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis [Beetle & A. Young] S. L. Welsh) steppe communities that had similar soils, topography, climate, and management. Noninvaded plant communities had greater cover and density of all native herbaceous functional groups compared to medusahead-invaded communities (P < 0.01). Large perennial grass cover was 15-fold greater in the noninvaded compared to invaded plant communities. Sagebrush cover and density were greater in the noninvaded compared to the medusahead-invaded communities (P < 0.01). Biomass production of all native herbaceous functional groups was higher in noninvaded compared to invaded plant communities (P < 0.02). Perennial and annual forb biomass production was 1.9- and 45-fold more, respectively, in the noninvaded than invaded communities. Species richness and diversity were greater in the noninvaded than invaded plant communities (P < 0.01). The results of this study suggest that medusahead invasion substantially alters vegetation characteristics of sagebrush steppe plant communities, and thereby diminishes wildlife habitat, forage production, and ecosystem functions. Because of the broad negative influence of medusahead invasion, greater efforts should be directed at preventing its continued expansion.     

Evaluating the quality of street trees in Washington,D.C.: Implications for environmental justice

Urban street trees are part of the bundle of environmental amenities that support healthy social, economic, and environmental functions. In this study, we systematically evaluate the quality of 196,825 street trees at the US. Census tract level in Washington D.C., as well as related impacts from socioeconomic, landscape patterns and environmental factors using Ordinary least-squares (OLS) regression, geographically weighted regression (GWR) and structural equation modeling (SEM). Our results reveal that environmental and socioeconomic factors can explain most of the spatial variation of street tree quality in Washington, D.C. There is a substantial statistical negative relationship between median household income and the percent of street trees under stress, which provided the evidence of the inequities of street tree quality in Washington D.C. Higher-income neighborhoods exhibited a lower proportion of street trees under stress. In addition, the extreme summer temperature is positively associated with the proportion of street trees under stress. The quality of street trees is directly impacted by environmental and landscape pattern factors. There is also an indirect impact from socioeconomic factor toward quality of street trees. Our findings suggest that multiple variables, related to income, age, education, landscape pattern, and environment contribute to the quality of street trees in D.C. Based upon our findings, we identify strategies and insights for urban street tree management in DC to not only address environmental inequity and injustice, but also promote a more inclusive and resilient urban greenery system.     

FlorTree: A unifying modelling framework for estimating the species-specific pollution removal by individual trees and shrubs

Atmospheric pollution is a threatening problem around the world, with tropospheric ozone (O₃), nitrogen dioxide (NO₂) and particulate matter (PM₁₀) among the most harmful pollutants for citizens’ health. Nature-based solutions such as urban trees can cut down air concentrations of these pollutants thanks to stomatal uptake and dry deposition on their canopies and, in addition, uptake carbon dioxide (CO₂) and store carbon in their tissues. Unfortunately, some species emit biogenic Volatile Organic Compounds (bVOCs) that are O₃-precursors leading to air quality deterioration. As a proper selection of species is essential for urban greening, we developed an innovative single-tree model (FlorTree) to estimate the maximum flux of air pollutants. FlorTree considered species-specific parameters, such as tree morphology (height and crown leaf area), leaf/shoot structure, leaf habit (deciduous/evergreen) and eco-physiological responses to environmental factors, for 221 urban tree and shrub species. We applied the FlorTree model to examine i) which are the best species for air pollution removal in the case study of Florence (Italy) and ii) whether the species-specific removal performance is affected by different climate and air pollution conditions in other cities, namely Bucharest (Romania) and Tokyo (Japan). Results suggested that 24 tall trees (mainly broadleaves belonging to Tilia, Acer and Fraxinus genus) may be recommended for Florence due to their large crowns at maturity (50 years old), relatively high stomatal conductance and no bVOCs release. These general characteristics, however, were affected by climatic and pollutant conditions, suggesting that FlorTree must be applied to the local conditions. Therefore, our results demonstrated that FlorTree can be applied in any city for maximizing the air quality improvement by urban trees.     

The effects of applied water at various fractions of measured evapotranspiration on water relations and vegetative growth of Thompson Seedless grapevines

Vegetative growth and water relations of Thompson Seedless grapevines in response to applied water amounts at various fractions of measured grapevine ET_c were quantified. Treatments ranged from no applied water up to 1.4 times the water used by vines growing in a weighing lysimeter. All treatments were irrigated at the same frequency as the vines in the lysimeter (whenever they used 2 mm of water), albeit at their respective fraction. Soil water content and midday leaf water potential (Ψ_l) were measured routinely in four of the irrigation treatments across years. The amount of water depleted in the soil profile ranged from 190 mm for the 0.2 treatment in 1993 to no water depletion for the 1.4 treatment in 1992. The irrigation treatments significantly affected midday Ψ_l, total shoot length, leaf area per vine, pruning weights and trunk diameter; as applied water decreased so did vegetative growth. Pruning weights were a linear function of the seasonal, mean midday Ψ_l across growing seasons. The application of water amounts in excess of evapotranspiration negatively affected vegetative growth some of the years. A companion paper will demonstrate that over-irrigation can negatively affect reproductive growth of this grape cultivar due to excess vegetative growth.     

Drainage performance and soil management

The performance of installed subsurface drainage systems is considerably influenced by soil management practices. These influences can be both positively and negatively. Cases of such influences are discussed in this paper. Optimal rootzone aeration and soil workability will often require a combination of drainage and soil management improvements.     

基于压力-状态-响应模型的农业生态系统健康评价方法

农业是经济发展与环境保护矛盾最突出的区域,农业生态系统健康评价作为农业可持续发展的基础研究,应得到足够的重视。本文根据农业生态系统的特征和压力-状态-响应（PSR）模型,选取了若干较为公认的反映农业生态健康的指标,依据其意义建立了类型识别的物元评判模型。应用于大兴区7个乡镇,得到了以下结论：农业生态系统处在“健康”标准的有魏善庄镇、礼贤镇;处在“临界状态”标准的有长子营镇、安定镇、瀛海镇;处在“不健康”标准的有西红门镇、旧宫镇。评价结果基本与实际相符,说明建立的评价方法是切实可行的。     

The future of fish passage science,engineering, and practice

Much effort has been devoted to developing, constructing and refining fish passage facilities to enable target species to pass barriers on fluvial systems, and yet, fishway science, engineering and practice remain imperfect. In this review, 17 experts from different fish passage research fields (i.e., biology, ecology, physiology, ecohydraulics, engineering) and from different continents (i.e., North and South America, Europe, Africa, Australia) identified knowledge gaps and provided a roadmap for research priorities and technical developments. Once dominated by an engineering‐focused approach, fishway science today involves a wide range of disciplines from fish behaviour to socioeconomics to complex modelling of passage prioritization options in river networks. River barrier impacts on fish migration and dispersal are currently better understood than historically, but basic ecological knowledge underpinning the need for effective fish passage in many regions of the world, including in biodiversity hotspots (e.g., equatorial Africa, South‐East Asia), remains largely unknown. Designing efficient fishways, with minimal passage delay and post‐passage impacts, requires adaptive management and continued innovation. While the use of fishways in river restoration demands a transition towards fish passage at the community scale, advances in selective fishways are also needed to manage invasive fish colonization. Because of the erroneous view in some literature and communities of practice that fish passage is largely a proven technology, improved international collaboration, information sharing, method standardization and multidisciplinary training are needed. Further development of regional expertise is needed in South America, Asia and Africa where hydropower dams are currently being planned and constructed.